Is this the right bid???

You don't mention the scope of work for these bids. Are you asking them to repair an existing deck, tear one down, build a new one, replace floor, or whatever? I can't wrap my head around a competent builder constructing a redwood deck to code for $7 per square foot, I doubt he could buy the decking and rails for that price, let alone install it. So either you are getting an incredible deal, or there is something seriously wrong with the bid, or the scope is totally different. Sometimes things that are too good to believe, are too good to believe.